Mechanical Properties of Textured Alumina Prepared by Colloidal Processing in a Strong Magnetic Field
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Mechanical Properties of Textured Alumina Prepared by Colloidal Processing in a Strong Magnetic Field Tohru S. Suzuki, Tetsuo Uchikoshi, Koji Morita, Keijiro Hiraga, and Yoshio Sakka Nano Ceramics Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, 3050047, Japan
INTRODUCTION Anisotropic designs of ceramics have attracted attention, because of their improved electrical, mechanical and other properties. Texture structured ceramics have been produced by hot forming, Templated Grain Growth (TGG) and so on. However, shape and orientation direction are limited, when using these techniques. On the other hand, we have reported that development of texture can be controlled by slip casting in a strong magnetic field followed by heating even for diamagnetic ceramics such as alumina. We report in this paper the mechanical properties of the textured alumina produced by a slip casting or electrophoretic deposition in a strong magnetic field EXPERIMENT The starting material was high-purity, spherical, single crystalline alumina powder with particle diameter averaging 0.2 µm. The alumina powder was dispersed in a suspension by using an ultrasonic homogenizer and a magnetic stirrer. The suspension was placed in a superconducting magnet with a room temperature bore of 100mm, and then a strong magnetic field of 12T was applied to the suspension to rotate each particle by a magnetic torque attributed to the anisotropic susceptibility during slip casting. Furthermore, Electrophoretic deposition (EPD) is also applied to shaping textured ceramics from stable colloidal suspension which is placed in a strong magnetic field (Fig.1). The sintering was conducted at the desired temperature for 2h in air without a magnetic field. RESULTS AND DISCUSSION We confirmed in our previous reports that c-axis of alumina with the trigonal unit cell was parallel to the direction of magnetic field. Bending strength was measured and hightemperature tensile tests were carried out. Bending strength of textured alumina depended on the direction of oriented microstructure. When the angle between the direction of the oriented c-axis and the tensile axis was 45 degree in tensile tests, the flow stress of textured alumina was inferior to that of random oriented alumina, and the tensile elongation was superior to that of random oriented alumina. We have reported that alumina/alumina laminar composites with different crystalline-oriented layer are produced by EPD in a strong magnetic field. The direction of the electric field relative to the magnetic field was altered to control the dominant crystal faces. The sintering was
conducted at 1873K for 2h in air without a magnetic field. The composite with different crystalline-oriented layer was fabricated by alternately changing the angle between the directions of the magnetic and electric fields layer by layer during EPD in 10T (Fig. 2). Bending strength of laminar composite depended on the direction of multilayered microstructure. Crack was propagated by bending in a zig-zag path.
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